fat bass is easiest to get with a real analog synth, such as a roland juno 106. just keep in mind that most analog synths are monophonic (unless you spend a fortune), which means they can only make one sound at a time.

the new digital synths, like the access virus, can often play up to 16 parts at once, meaning less clutter in your studio.

you can use either plugins or hardware bass enhancers to fatten up your bass, but once again, it's better if you learn how to make good bass in the first place. better sounds sooner, with less processing later, is a good general rule.

something else worth noting - get some good near field monitors if you don't already have some. they may seem expensive up front and you might prefer to spend the money on actual instruments, but if you can't hear what you are doing, you'll never get the results you are after. they make a huge difference.